Retractable safety needles for medical applications

• US 6,379,337 B1
• Filed: 12/23/1999
• Issued: 04/30/2002
• Est. Priority Date: 12/22/1998
• Status: Expired due to Fees

• Current Assignee: Mohammad M. B. B. S., Owais
• Original Assignee: Mohammad M. B. B. S., Owais
• Inventors: Mohammad M. B. B. S., Owais
• Primary Examiner(s): Dawson, Glenn K.
• Assistant Examiner(s): MAYNARD, JENNIFER J
• Application Number:
  US09/471,094
• Time in Patent Office: 859 Days
• Field of Search: 604/263, 604/264, 604/272, 604/187, 604/162, 604/163, 604/195, 606/167, 606/185, 606/187
• US Class Current: 604/195
• CPC Class Codes: A61B 5/15003 for venous or arterial blood
• CPC Class Codes: A61B 5/150236 Pistons, i.e. cylindrical bodies that sit inside the syringe barrel, typically with an air tight seal, and slide in the barrel to create a vacuum or to expel blood
• CPC Class Codes: A61B 5/150404 Specific design of proximal end
• CPC Class Codes: A61B 5/150496 Details of construction of hub, i.e. element used to attach the double-ended needle to a piercing device or sampling device
• CPC Class Codes: A61B 5/150519 Details of construction of hub, i.e. element used to attach the single-ended needle to a piercing device or sampling device
• CPC Class Codes: A61B 5/150572 Pierceable protectors, e.g. shields, caps, sleeves or films, e.g. for hygienic purposes
• CPC Class Codes: A61B 5/150633 Protective sleeves which are axially extensible, e.g. sleeves connected to, or integrated in, the piercing or driving device; pivotable protective sleeves
• CPC Class Codes: A61B 5/150717 manually removed
• CPC Class Codes: A61B 5/150732 Needle holders, for instance for holding the needle by the hub, used for example with double-ended needle and pre-evacuated tube,
• CPC Class Codes: A61B 5/1545 comprising means for indicating vein or arterial entry
• CPC Class Codes: A61M 2005/3228 the needle being retracted by a member protruding laterally through a slot in the barrel, e.g. double-ended needles
• CPC Class Codes: A61M 5/322 Retractable needles, i.e. disconnected from and withdrawn into the syringe barrel by the piston devices for protecting guide needles in combination with catheters A61M25/0612
• CPC Class Codes: A61M 5/3232 Semi-automatic needle retraction, i.e. in which triggering of the needle retraction requires a deliberate action by the user, e.g. manual release of spring-biased retraction means
• CPC Class Codes: A61M 5/3257 Semi-automatic sleeve extension, i.e. in which triggering of the sleeve extension requires a deliberate action by the user, e.g. manual release of spring-biased extension means
• CPC Class Codes: A61M 5/3272 having projections following labyrinth paths
• CPC Class Codes: A61M 5/34 Constructions for connecting the needle , e.g. to syringe nozzle or needle hub connecting catheter tubes to hubs A61M25/0014

Abstract

A retractable needle for use with a catheter, featuring a cylindrical hub having a hollow needle extending through the hub. The hub has a flash chamber connected thereto where the interior of the needle is in fluid communication with the interior of the flash chamber. The hub is slidably positioned in a housing having a wall with a longitudinal slot therein. A stem connected with the hub passes through the slot, and has a thumbrest rigidly fixed thereto, where the thumbrest may be used to manually move the knob from a first locking position, where the needle is retracted within the housing, to a second locking position where the needle is exposed. A catheter is mounted on the needle when the needle is exposed. Also disclosed are blood-drawing needles comprising a cylindrical hub having a hollow needle extending from one end of the hub. The hub has a cavity adapted to frictionally engage the tip of a syringe barrel on its other end. The hub is slidably positioned in a housing having a wall with a longitudinal slot therein. A stem connected with the hub passes through the slot, and has a thumbrest rigidly fixed thereto, where the thumbrest may be used to manually move the knob from a first locking position, where the needle is retracted within the housing, to a second locking position where the needle is exposed.

Claims

1. A retractable needle in combination with a catheter, comprising:

a) a needle assembly comprising;

a cylindrical hub having an anterior end and a posterior end;

a hollow needle extending through the hub and projecting from the anterior end of the hub;

a tubular flash chamber having a first end which is connected in a leakproof fashion with the posterior end of the hub, and a second end; and

a stem having a defined diameter rigidly connected with said hub, said stem being non-rotatable relative to said hub, wherein said stem has a thumbrest rigidly fixed to the stem at a defined distance from the hub;

where an interior of the hollow needle is in fluid communication with an interior of said tubular flash chamber;

b) a housing with a defined longitudinal axis having a tubular wall with a longitudinal slot which is wider than the diameter of the stem therein, said housing having a first end and a second end, wherein the first end of the housing has an opening adapted to allow the hollow needle to pass therethrough and the second end of the housing is closed;

said housing having said needle assembly mounted therein so that the stem is slidably engaged by the longitudinal slot, so that said needle assembly may be moved from a first position where the needle passes through the opening in the first end of the housing and is exposed to a second position where the needle is within the housing by sliding the stem toward the second end of the housing and causing the needle to retract through the opening in the first end of the housing;

c) a means for reversibly locking the stem at a first defined location in said longitudinal slot so as to hold said needle assembly in said first position;

wherein the means for reversibly locking the stem at the first defined location comprises a first transverse slot intersecting the longitudinal slot at the first defined location, and a first pair of teeth on opposite sides of the first transverse slot;

wherein a locking position is defined between the first pair of teeth and a closed end of the first transverse slot; and

wherein the first pair of teeth are separated by a distance which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the first pair of teeth;

d) a means for reversibly locking the stem at a second defined location in said longitudinal slot so as to hold said needle assembly in said second position;

e) a catheter which is supported by the needle when the needle is in the first position; and

f) a means for removably fastening the catheter to the first end of the housing;

where the hub of said needle assembly is movably positioned along the defined longitudinal axis of the housing.

2. The retractable needle of claim 1, wherein the housing is manufactured from two parts.

3. The retractable needle of claim 2, wherein the housing is manufactured from:

a first part, comprising a hollow tube having a first end adapted to admit the hollow needle and a second end adapted to admit the needle assembly, said second end having a male joint on its outer surface; and

a second part, comprising a cap having a female joint adapted to be fitted onto the male joint;

wherein the longitudinal slot in the housing runs along the length of the hollow tube from the first defined location near the first end of the hollow tube to the second end of the hollow tube, with the longitudinal slot being closed at the first end of the hollow tube and having an opening at the second end of the hollow tube, said opening being adapted to admit the stem on the needle assembly;

and wherein the longitudinal slot comprises the means for reversibly locking the stem at the first defined location near the first end of the hollow tube, and the means for reversibly locking the stem at the second defined location near the second end of the hollow tube.

4. The retractable needle of claim 3, wherein the cap is fitted onto the joint at the second end of the hollow tube and acts to close the opening in the longitudinal slot.

5. The apparatus of claim 4, wherein the means for reversibly locking the stem at the second defined location comprises a second transverse slot intersecting the longitudinal slot at the second defined location, and a second pair of teeth on opposite sides of the second transverse slot;

wherein a second locking position is defined between the second pair of teeth and a closed end of the second transverse slot; and

wherein the second pair of teeth are separated by a distance which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the second pair of teeth.

6. The apparatus of claim 5, wherein a spring acts to bias the stem away from the first defined location toward the second defined location.

7. The apparatus of claim 4, wherein the means for reversibly locking the stem at the second defined location comprises a second pair of teeth on opposite sides of the longitudinal slot at the second defined location;

wherein a second locking position is defined by the second pair of teeth and the cap closing the open end of the longitudinal slot; and

wherein the second pair of teeth are separated by a distance which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the second pair of teeth.

8. The apparatus of claim 7, wherein a spring acts to bias the stem away from the first defined location toward the second defined location.

9. The retractable needle of claim 4, wherein the means for reversibly locking the stem at the second defined location comprises a second pair of teeth on opposite sides of the longitudinal slot, said second pair of teeth being positioned near the second defined location;

wherein a second locking position is defined between the second pair of teeth and the cap fitted onto the joint at the second end of the hollow tube.

10. The apparatus of claim 1, wherein the hub has a diameter which is the same as an inner diameter of the housing.

11. The apparatus of claim 1, wherein the hub has a diameter which is less than an inner diameter of the housing.

12. The apparatus of claim 11, wherein the thumbrest is positioned outside of the housing, and is too wide to pass through the longitudinal slot engaging the stem, and

wherein the stem connecting the thumbrest to the hub is sufficiently long to allow the hub to be positioned along the longitudinal axis of the housing.

13. The apparatus of claim 1, wherein the thumbrest is planar.

14. The apparatus of claim 1, wherein the thumbrest is a ring around the tubular housing.

15. A retractable needle, comprising:

a) a needle assembly comprising;

a cylindrical hub having an anterior end and a posterior end, said posterior end of said hub having a frusto-conical cavity therein, said cavity being adapted to frictionally engage a fitting on a syringe barrel;

a hollow needle extending through the hub and projecting from the anterior end of the hub; and

a stem having a defined diameter connected with said hub, said stem having a thumbrest rigidly fixed to the stem at a defined distance from the hub;

b) a housing with a defined longitudinal axis having a tubular wall with a longitudinal slot which is wider than the diameter of the stem therein, said housing having a first end and a second end, wherein the first end has an opening adapted to allow the hollow needle to pass therethrough and the second end has an opening adapted to admit the syringe barrel;

said housing having said needle assembly mounted therein so that the stem is slidably engaged by the longitudinal slot, so that said needle assembly may be moved from a first position where the needle passes through the opening in the first end of the housing and is exposed to a second position where the needle is within the housing by sliding the stem toward the second end of the housing and causing the needle to retract through the opening in the first end of the housing;

c) a means for reversibly locking the stem at a first defined location in said longitudinal slot so as to hold said needle assembly in said first position;

d) a means for reversibly locking the stem at a second defined location in said longitudinal slot so as to hold said needle assembly in said second position; and

where the hub of said needle assembly is movably positioned along the defined longitudinal axis of the housing.

16. The retractable needle of claim 15, wherein the housing is manufactured from two parts, comprising a hollow tube having a first end adapted to admit the hollow needle and a second end adapted to admit the needle assembly, said second end having a male joint on its outer surface;

and a ring having a female joint adapted to be fitted onto the male joint.

17. The apparatus of claim 15, wherein the thumbrest is planar.

18. The apparatus of claim 15, wherein the thumbrest is a ring around the tubular housing.

23. The apparatus of claim 15, wherein the hub has a diameter which is the same as an inner diameter of the housing.

24. The apparatus of claim 15, wherein the hub has a diameter which is less than an inner diameter of the housing.

25. The apparatus of claim 24, wherein the thumbrest is positioned outside of the housing, and is too wide to pass through the longitudinal slot engaging the stem, and

wherein the stem connecting the thumbrest to the hub is sufficiently long to allow the hub to be positioned along the longitudinal axis of the housing.

19. A retractable needle, comprising:

a) a needle assembly comprising;

a cylindrical hub having an anterior end and a posterior end, said posterior end of said hub having a frusto-conical cavity therein, said cavity being adapted to frictionally engage a fitting on a syringe barrel;

a hollow needle extending through the hub and projecting from the anterior end of the hub; and

a stem having a defined diameter connected with said hub, said stem having a thumbrest rigidly fixed to the stem at a defined distance from the hub;

b) a housing with a defined longitudinal axis having a tubular wall with a longitudinal slot which is wider than the diameter of the stem therein, said housing having a first end and a second end, wherein the first end has an opening adapted to allow the hollow needle to pass therethrough and the second end has an opening adapted to admit the syringe barrel;

said housing having said needle assembly mounted therein so that the stem is slidably engaged by the longitudinal slot, so that said needle assembly may be moved from a first position where the needle passes through the opening in the first end of the housing and is exposed to a second position where the needle is within the housing by sliding the stem toward the second end of the housing and causing the needle to retract through the opening in the first end of the housing;

c) a means for reversibly locking the stem at a first defined location in said longitudinal slot so as to hold said needle assembly in said first position;

d) a means for reversibly locking the stem at a second defined location in said longitudinal slot so as to hold said needle assembly in said second position; and

where the hub of said needle assembly is movably positioned along the defined longitudinal axis of the housing; and

wherein the housing is manufactured from;

a first part, comprising a hollow tube having a first end adapted to admit the hollow needle and the second end adapted to admit the needle assembly, said second end having the male joint on its outer surface; and

the second part, comprising a ring having a female joint adapted to be fitted onto the male joint;

wherein the longitudinal slot in the housing runs along the length of the hollow tube from the first defined location near the first end of the hollow tube to the second end of the hollow tube, with the longitudinal slot being closed at the second end of the hollow tube and having an opening at the second end of the hollow tube, said opening being adapted to admit the stem on the needle assembly;

and wherein the longitudinal slot comprises a means for reversibly locking the stem at the first defined location near the first end of the hollow tube, and a means for reversibly locking the stem at the first defined location near the second end of the hollow tube.

20. The retractable needle of claim 19, wherein the ring is fitted onto the joint at the second end of the hollow tube and acts to close the opening in the longitudinal slot.

21. The retractable needle of claim 20, wherein the means for reversibly locking the stem at the first defined location comprises a first pair of teeth on opposite sides of the longitudinal slot, said first pair of teeth being positioned near the first defined location;

wherein a locking position is defined between the first pair of teeth and the closed end of the longitudinal slot; and

wherein the first pair of teeth cause the width of the longitudinal slot to narrow to a width which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the first pair of teeth.

22. The retractable needle of claim 21, wherein the means for reversibly locking the stem at the second defined location comprises a second pair of teeth on opposite sides of the longitudinal slot, said second pair of teeth being positioned near the second defined location;

wherein a locking position is defined between the second pair of teeth and the ring fitted onto the joint at the second end of the hollow tube; and

wherein the second pair of teeth cause the width of the longitudinal slot to narrow to a width which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the second pair of teeth.

26. A retractable needle, comprising:

a) a needle assembly comprising;

a cylindrical hub having an anterior end and a posterior end;

a hollow needle extending through the hub, said needle having a first end adapted to penetrate a blood vessel projecting from the anterior end of the hub and a second end projecting from the posterior end of the hub; and

a stem having a defined diameter connected with said hub, said stem having a thumbrest rigidly fixed to the stem at a defined distance from the hub;

b) a housing with a defined longitudinal axis having a tubular wall with a longitudinal slot which is wider than the diameter of the stem therein, said housing having a first end and a second end, wherein the first end has an opening adapted to allow the first end of the hollow needle to pass therethrough, and the second end has an opening adapted to admit an evacuated blood collection tube, said blood collection tube having an elastomeric seal adapted to be penetrated by the second end of the hollow needle;

said housing having said needle assembly mounted therein so that the stem is slidably engaged by the longitudinal slot, so that said needle assembly may be moved from a first position where the needle passes through the opening in the first end of the housing and is exposed to a second position where the needle is within the housing by sliding the stem toward the second end of the housing and causing the needle to retract through the opening in the first end of the housing;

c) a means for reversibly locking the stem at a first defined location in said longitudinal slot so as to hold said needle assembly in said first position;

d) a means for reversibly locking the stem at a second defined location in said longitudinal slot so as to hold said needle assembly in said second position; and

e) a means for preventing blood from flowing through the needle when the first end of the needle penetrates the blood vessel unless the second end of the needle penetrates the seal on the blood collection tube;

where the hub of said needle assembly is movably positioned along the defined longitudinal axis of the housing.

27. The retractable needle of claim 26, wherein the housing is manufactured from two parts.

28. The retractable needle of claim 27, wherein the housing is manufactured from:

a first part, comprising a hollow tube having a first end adapted to admit the hollow needle and a second end adapted to admit the needle assembly, said second end of the first part having a male joint on its outer surface; and

a second part, comprising a ring having a female joint adapted to be fitted onto the male joint;

wherein the longitudinal slot in the housing runs along the length of the hollow tube from a first defined location near the first end of the hollow tube to the second end of the hollow tube, with the longitudinal slot being closed at the first end of the hollow tube and having an opening at the second end of the hollow tube, said opening being adapted to admit the stem on the needle assembly;

and wherein the longitudinal slot comprises the means for reversibly locking the stem at the first defined location near the first end of the hollow tube, and the means for reversibly locking the stem at the second defined location near the second end of the hollow tube.

29. The retractable needle of claim 28, wherein the ring is fitted onto the joint at the second end of the hollow tube and acts to close the opening in the longitudinal slot.

30. The retractable needle of claim 29, wherein the means for reversibly locking the stem at the first defined location comprises a first pair of teeth on opposite sides of the longitudinal slot, said first pair of teeth being positioned near the first defined location;

wherein a locking position is defined between the first pair of teeth and the closed end of the longitudinal slot; and

wherein the first pair of teeth cause the width of the longitudinal slot to narrow to a width which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the first pair of teeth.

31. The retractable needle of claim 29, wherein the means for reversibly locking the stem at the second defined location comprises a second pair of teeth on opposite sides of the longitudinal slot, said second pair of teeth being positioned near the second defined location;

wherein a locking position is defined between the second pair of teeth and the cap fitted onto the joint at the second end of the hollow tube; and

wherein the second pair of teeth cause the width of the longitudinal slot to narrow to a width which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the second pair of teeth.

32. The apparatus of claim 26, wherein the hub has a diameter which is the same as an inner diameter of the housing.

33. The apparatus of claim 26, wherein the hub has a diameter which is less than an inner diameter of the housing.

34. The apparatus of claim 33, wherein the thumbrest is positioned outside of the housing, and is too wide to pass through the longitudinal slot engaging the stem, and wherein the stem connecting the thumbrest to the hub is sufficiently long to allow the hub to be positioned along the longitudinal axis of the housing.

35. The apparatus of claim 26, wherein the thumbrest is planar.

36. The apparatus of claim 26, wherein the thumbrest is a ring around the tubular housing.

37. A retractable needle, comprising:

a) a needle assembly comprising;

a cylindrical hub having an anterior end and a posterior end, said posterior end of said hub having a frusto-conical cavity therein, said cavity being adapted to frictionally engage a fitting on a syringe barrel;

a hollow needle extending through the hub and projecting from the anterior end of the hub; and

a stem having a defined diameter connected with said hub, said stem having a thumbrest rigidly fixed to the stem at a defined distance from the hub;

b) a housing with a defined longitudinal axis having a tubular wall with a longitudinal slot which is wider than the diameter of the stem therein, said housing having a first end and a second end, wherein the first end has an opening adapted to allow the hollow needle to pass therethrough and the second end has an opening adapted to admit the syringe barrel;

wherein said longitudinal slot has a first closed end near the first end of the housing and a second open end at the second end of the housing;

said housing having said needle assembly mounted therein so that the stem is slidably engaged by the longitudinal slot, so that said needle assembly may be moved from a first position where the needle passes through the opening in the first end of the housing and is exposed to a second position where the needle is within the housing by sliding the stem toward the second end of the housing and causing the needle to retract through the opening in the first end of the housing;

c) a means for closing the second open end of the longitudinal slot;

d) a means for reversibly locking the stem at a first defined location in said longitudinal slot so as to hold said needle assembly in said first position; and

e) a means for reversibly locking the stem at a second defined location in said longitudinal slot so as to hold said needle assembly in said second position;

wherein the means for reversibly locking the stem at the first defined location comprises a first pair of teeth on opposite sides of the longitudinal slot, said first pair of teeth being positioned near the first defined location;

wherein a locking position is defined between the first pair of teeth and a first closed end of the longitudinal slot; and

wherein the first pair of teeth causes the width of the longitudinal slot to narrow to a width which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the first pair of teeth; and

wherein the means for reversibly locking the stem at the second defined location comprises a second pair of teeth on opposite sides of the longitudinal slot, said second pair of teeth being positioned near the second defined location;

wherein a locking position is defined by the second pair of teeth and the means for closing the second open end of the longitudinal slot; and

wherein the second pair of teeth causes the width of the longitudinal slot to narrow to a width which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the second pair of teeth.

38. A retractable needle for use with a catheter, comprising:

a) a needle assembly comprising;

a cylindrical hub having an anterior end and a posterior end;

a hollow needle extending through the hub and projecting from the anterior end of the hub;

a tubular flash chamber having a first end which is connected in a leakproof fashion with the posterior end of the hub, and a second end; and

a stem having a defined diameter rigidly connected with said hub, said stem being non-rotatable relative to said hub, wherein said stem has a thumbrest rigidly fixed to the stem at a defined distance from the hub;

where an interior of the hollow needle is in fluid communication with an interior of said tubular flash chamber;

b) a housing with a defined longitudinal axis having a tubular wall with a longitudinal slot which is wider than the diameter of the stem therein, said housing having a first end of the housing and a second end, wherein the first end has an opening adapted to allow the hollow needle to pass therethrough and the second end of the housing is closed;

said housing having said needle assembly mounted therein so that the stem is slidably engaged by the longitudinal slot, so that said needle assembly may be moved from a first position where the needle passes through the opening in the first end of the housing and is exposed to a second position where the needle is within the housing by sliding the stem toward the second end of the housing and causing the needle to retract through the opening in the first end of the housing;

c) a means for reversibly locking the stem at a first defined location in said longitudinal slot so as to hold said needle assembly in said first position;

wherein the means for reversibly locking the stem at the first defined location comprises a first transverse slot intersecting the longitudinal slot at the first defined location, and a first pair of teeth on opposite sides of the first transverse slot;

wherein a locking position is defined between the first pair of teeth and a closed end of the first transverse slot; and

wherein the first pair of teeth are separated by a distance which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the first pair of teeth;

d) a means for reversibly locking the stem at a second defined location in said longitudinal slot so as to hold said needle assembly in said second position; and

f) a means for removably fastening a catheter to the first end of the housing;

wherein the needle is adapted to releasably engage a catheter when the needle assembly is in the first position and the needle is exposed; and

where the hub of said needle assembly is movably positioned along the defined longitudinal axis of the housing.

39. A retractable needle for use with a catheter, comprising:

a) a hollow needle;

b) a cylindrical hub, said hollow needle passing axially through said cylindrical hub;

c) an adjustable-length tube having a first end and a second end, said tube having a length which may be reversibly altered from a first contracted length to a second extended length;

d) a flash chamber having a first end which is sealed to the first end of the adjustable-length tube so that an interior of the flash chamber is in fluid communication with an interior of the adjustable-length tube;

e) a means for securing the cylindrical hub to the second end of the adjustable-length tube so that an interior of the hollow needle is in fluid communication with the interior of the adjustable-length tube;

f) a tubular sheath disposed around the adjustable-length tube;

said tubular sheath having a first end which is rigidly connected with both the first end of the adjustable length tube and the flash chamber, and a second end having an opening adapted to allow the hollow needle to pass therethrough; and

g) a means for reversibly altering the length of the adjustable-length tube from the first contracted length to the second extended length;

where the needle is entirely disposed within the sheath when the adjustable-length tube is contracted, and where the needle is exposed through the opening in the second end of the sheath when the adjustable-length tube is extended; and

where the hollow needle is adapted to engage a cannula of a catheter when the needle is exposed.

40. The apparatus of claim 39, wherein the means for reversibly altering the length of the adjustable-length tube comprises a knob having a defined diameter which is connected with the hub, and a longitudinal slot in the tubular sheath, where the longitudinal slot is wider than the diameter of the knob, and the knob is slidably engaged by the longitudinal slot;

a means for reversibly locking the knob at a first defined location which causes the needle to be exposed; and

a means for reversibly locking the knob at a second defined location which causes the needle to be disposed within the sheath.

41. The apparatus of claim 40, wherein the means for reversibly locking the knob at the first defined location comprises a first pair of teeth on opposite sides of the longitudinal slot, said first pair of teeth being positioned near the first defined location;

wherein a locking position is defined between the first pair of teeth and a first closed end of the longitudinal slot; and

wherein the first pair of teeth causes the width of the longitudinal slot to narrow to a width which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the first pair of teeth; and

wherein the means for reversibly locking the stem at the second defined location comprises a second pair of teeth on opposite sides of the longitudinal slot, said second pair of teeth being positioned near the second defined location;

wherein a locking position is defined by the second pair of teeth and a means for closing a second end of the longitudinal slot; and

wherein the second pair of teeth causes the width of the longitudinal slot to narrow to a width which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the second pair of teeth.

42. A retractable syringe needle, comprising:

a) a hollow hypodermic needle;

b) a cylindrical hub, said hollow needle passing axially through said cylindrical hub;

c) an adjustable-length tube having a first end and a second end, said tube having a length which may be reversibly altered from a first contracted length to a second extended length;

d) a means for reversibly securing a syringe barrel having a frusto-conical fitting thereon to the first end of the adjustable-length tube so that an interior of the syringe barrel is in fluid communication with an interior of the adjustable-length tube;

e) a means for securing the cylindrical hub to the second end of the adjustable-length tube so that an interior of the hollow needle is in fluid communication with the interior of the adjustable-length tube;

f) a tubular sheath disposed around the adjustable-length tube;

said tubular sheath having a first end which is rigidly connected with the first end of the adjustable length tube, and a second end having an opening adapted to allow the hollow hypodermic needle to pass therethrough; and

g) a means for reversibly altering the length of the adjustable-length tube from the first contracted length to the second extended length;

wherein the hypodermic needle is entirely disposed within the sheath when the adjustable-length tube is contracted, and where the hypodermic needle is exposed through the opening in the second end of the sheath when the adjustable-length tube is extended;

wherein the means for reversibly altering the length of the adjustable-length tube comprises;

a knob having a defined diameter which is connected with the hub, and a longitudinal slot in the tubular sheath, where the longitudinal slot is wider than the diameter of the knob, and the knob is slidably engaged by the longitudinal slot;

a means for reversibly locking the knob at a first defined location which causes the needle to be exposed; and

a means for reversibly locking the knob at a second defined location which causes the needle to be disposed within the sheath;

wherein the means for reversibly locking the knob at the first defined location comprises a first pair of teeth on opposite sides of the longitudinal slot, said first pair of teeth being positioned near the first defined location;

wherein a locking position is defined between the first pair of teeth and a first closed end of the longitudinal slot; and

wherein the first pair of teeth causes the width of the longitudinal slot to narrow to a width which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the first pair of teeth; and

wherein the means for reversibly locking the stem at the second defined location comprises a second pair of teeth on opposite sides of the longitudinal slot, said second pair of teeth being positioned near the second defined location;

wherein a locking position is defined by the second pair of teeth and a means for closing a second end of the longitudinal slot; and

wherein the second pair of teeth causes the width of the longitudinal slot to narrow to a width which is smaller than the diameter of the stem, but which is large enough to allow a user to push the stem through the second pair of teeth.